Cam-actuation system for variable displacement vane pump

ABSTRACT

A variable displacement vane pump has a plurality of vanes slidably fitted in slots formed substantially radially in a rotor. Two identical track elements are movably arranged around the rotor to provide a track for the vanes. The positions of the track elements determines the displacement of the pump. Each track element includes a radial inlet passage and a radial outlet passage. The inlet passage of one of the track elements is diametrically opposed from the inlet passage of the other of the track elements and the outlet passage of one of the track elements is diametrically opposed from the outlet passage of the other of the track elements in order to pressure balance the rotor. The track elements are slidably mounted within a frame around which is rotatably disposed a cam actuation ring. Cam follower members are provided on the cam ring to contact respective cam surfaces on the track elements and control the position of the track elements with respect to the rotor. The cam ring is rotated about the frame by means of pistons.

United States Patent Sundberg Feb. 15, 1972 CAM-ACTUATION SYSTEM FOR VARIABLE DISPLACEMENT VANE PUMP ZZZ 44 /&

Primary Examiner-Carlton R. Croyle Assistant Examiner-John J. Vrablik Attorney--Richard A. Damon [57] ABSTRACT A variable displacement vane pump has a plurality of vanes slidably fitted in slots fonned substantially radially in a rotor. Two identical track elements are movably arranged around the rotor to provide a track for the vanes. The positions of the track elements determines the displacement of the pump. Each track element includes a radial inlet passage and a radial outlet passage. The inlet passage of one of the track elements is diametrically opposed from the inlet passage of the other of the track elements and the outlet passage of one of the track elements is diametrically opposed from the outlet passage of the other of the track elements in order to pressure balance the rotor. The track elements are slidably mounted within a frame around which is rotatably disposed a cam actuation ring. Cam follower members are provided on the cam ring to contact respective cam surfaces on the track elements and control the position of the track elements with respect to the rotor. The cam ring is rotated about the frame by means of pistons.

3 Claims, 1 1 Drawing Figures PAIENTEBFEB 15 I972 SHEET 2 BF 4 F'IGJA INVENTOR JACK G. SUNDBYERG ATTORNEY PAIENT EDFEB 15 m2 3.642. 387

SHEET '4 [IF 4 INVENTOR JACK G. 'SUNDBERG BY Q W M ATTORNEY BACKGROUND OF THE INVENTION This invention relates to pumps and more particularly to variable displacement vane pumps.

Variable displacement vane pumps which employ movable track elements are known in the prior art. Typically these track elements are displaced with respect to the rotor by means of pistons fixably attached thereto. Variable displacement vane pumps are now being given serious consideration for inclusion in fuel-control systems. In existing fuel-control systems, pumping is performed by fixed displacement pumps. These pumps, which are ordinarily gear pumps, provide an output flow which exceeds engine fuel requirements under certain conditions. Therefore, means must be provided to bypass the excess flow back to the inlet of the pump. This bypassing of fuel engenders fuel heating which impairs the efficiency of the fuel control and creates other problems. Thus, it can be seen that replacement'of the existing fixed displacement pumps in fuel-control systems with variable displacement pumps would result in improved control system performance.

SUMMARY OF THE INVENTION The invention provides an actuation system for a variable displacement pump which enables the pump to match the gain of a system with which it is associated. In the case of a fuelcontrol system, the invention allows the output of the pump to meet the demands placed upon the fuel control.

In brief, the invention employs an actuation ring structure which is rotatably mounted around the track elements. The actuation ring and the track elements are respectively provided with cam follower members and cam surfaces which coact such that rotation of the actuation ring causes the track elements to assume different positions, thereby varying the displacement of the pump. By using this method of varying the position of the vane tracks, any flow to ring position function can be obtained by changing the cam surface contour. A device, such as a piston, is employed to rotate the actuation ring about the track elements.

Accordingly, it is a primary object of the invention to provide a means to change the output of a variable displacement vane pump in accordance with a predetermined function.

Another object is to provide a variable displacement vane pump in which the positions of the track elements are determined by the relative position ofa cam member.

Yet another object is to provide a variable displacement vane pump having two track elements with respective cam surfaces thereon which are positioned by an actuation ring having two cam members thereon which respectively engage the cam follower surfaces of the track elements to vary the output of the pump in accordance with the angular position of the actuation ring.

These and other objects will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a'schematic sectional elevational view of a pump according to the invention in a maximum displacement configuration.

FIG. IA is a fragmentary elevational section view of the pump of FIG. 1 showing the pump in a minimum displacement configuration.

FIG. 2 is a schematic longitudinal sectional view of the pump of FIG. 1 taken along the line 2--2.

FIG. 3 is an interior perspective view ofa track element of FIG. I.

FIG. 4 is an exterior perspective view of a track element of FIG. 1.

FIG. 5 is an elevational exploded view of the track elements of FIG. 1.

FIG. 6 is a perspective view of the frame of FIG. I.

FIG. 7 is an elevational view of a side plate of FIG. 2.

FIGS. 8 and 9 are sectional views taken along the lines 8-8 and 99, respectively, of FIG. 7.

FIG. 10 is a perspective view of a balance piston of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a vane pump 10 according to the instant invention in schematic form. With reference to FIG. 1, it is to be noted that the axial length of the pump 10 lies in a direction perpendicular to the plane of the paper. Pump 10 includes a housing 12 having a cavity or recess 14 therein, in which the basic elements of the pump are contained. An inlet conduit 16 communicates with the cavity 14 for delivering an input flow of a fluid, such as fuel, thereto. While the device shown in the drawings is intended to function as a pump and will be described as such, it will be understood that the design concept could be applied to a motor.

A rotor 18 is splined upon and driven by a drive shaft 20 which extends through the cavity 14, as more clearly shown in FIG. 2. If desired, shaft 20 could also be connected to an impeller pump which in turn would supply inlet fluid to inlet conduit 16, at the charging pressure required by the vane pump element, from a low pressure source such as an unpressurized tank. The charging pressure is defined as the inlet pressure required by the vane pump element to insure the vane spaces are completely filled with the pumped liquid. A plurality of vanes 22 are slideably mounted in slots 24 positioned around the periphery of rotor 18. The lower portions of the slots are referenced to discharge pressure by means described hereinafter to radially urge the vanes in an outward direction, thereby supplementing the centrifugal force.

The outer ends or tips of vanes 22 engage a smooth track surfacedefined by the inner periphery of two identical rigid track elements 26 and 28, the detailed structure of which is discussed hereinafter. The track elements 26 and 28 are slideably mounted within a frame structure 30 such that they are each movable in directions toward and away from the rotor.

Surrounding the frame 30 is a cam actuation ring 32 which is rotatable thereabout by actuator assemblies 34 and 36. The actuation ring 32 is provided with two cam follower members 38 and 40 which respectively coact with cam surfaces 42 and 44 disposed on the outer periphery of the track elements 26 and 28. The angular position of the actuation ring 32 as controlled by the actuator assemblies 34 and 36, determines the spacing between the track elements 26 and 28, and hence the displacement of the pump. In order to facilitate rotation of the actuation ring 38, balance pistons, respectively designated at 242 and 244, are located in the housing 12 to contact the respective outer peripheries of the track elements and urge them inwardly against the pressure forces exerted on their inner peripheries. It should be noted at this point that the balance pistons do not displace the track elements, but merely make rotation of the actuation ring easier, due to the reduced force of engagement between the cam surfaces 42 and 44 of the track elements and the respective cam follower members 38 and 40 of the actuation ring.

Turning now to FIG. 2, wherein the axial arrangement of the pump 10 is illustrated, it can be seen that at the axial ends of the cavity 14, end plates 46 and 48 are respectively positioned to seal the pump and port discharge pressure behind the vanes. End plate 46 is fixedly secured to the housing 12, whereas end plate 48 is mounted for sliding movement upon the shaft 20. A piston assembly 50 functions to pressure load the sideplate 48 in the direction of the side plate 46 to seal the pump. Discharge pressure is ported behind a spring-loaded piston 52, which is also slideable upon the shaft 20, to urge the piston 52 into engagement with the sideplate 48.

It will also be noted, with reference to FIG. 2, that the vane 22 is comprised of two segments, namely 22a and 22b to provide greater structural integrity, and to thereby reduce the possibility of vane failure. These vane segments are not structurally connected to one another. With respect to FIG. 2, it will also be noted that the slots 24 extend the full axial length of the rotor 18, and that the size of the pockets, formed between the radial inner extremities of the vanes and the slots, vary as a function of the radial displacement of the respective vanes.

Referring now to FIG. 1, in conjunction with FIGS. 3-5, wherein the detailed structure of the track elements 26 and 28 is shown, it should be noted that their inner peripheries 26a and 28a are contoured such that portions thereof are circularized, while other portions thereof form cam surfaces which interact with the vanes to cause the vanes to move radially in and out with respect to the slots. As previously mentioned, both of the track elements are identical structures.

As shown in FIG. 3, track element 26 includes two elongated curvilinear inlet passages 26b and 260 which permit inlet liquid to pass radially inward therethrough and fill the pockets formed between the adjacent vanes, the rotor, and surface 26a. These inlet passages extend completely through the track element and include recesses or channels in the track elements at their circumferential extremities. In contrast to the inlet passages 26b and 26c, outlet passages 26d and 26e extend only partially through the cam block 26, but include similar recesses or channels, and communicate with an axial discharge passage 26f which extends from one end of the element 26 to the other end thereof. Axial discharge passage 26f is an internal passage contained wholly within the track element 26. The discharge outlets 26g and 26h of the axial discharge passage 26f communicate with respective discharge conduits in the housing through mating apertures in the sideplates 46 and 48 which respectively confront these outlets.

The lips of track element 26 define a tongue and groove ar' rangement comprising tongues 26k and 26L and grooves 26i and 26j, this being discussed hereinafter. The corresponding elements of track element 28 are designated 28a- 28L. It will be noted from FIGS. 1 and 5 that when the track elements are engaged with one another, two areas of interdigitation are formed between the mating lips.

A specifically defined relationship exists between the circular arcs and cam arcs on the inner surfaces of the track elements and the radial inlet passages and discharge passages; the inlet and discharge areas are outlined by the solid doubleheaded arrows. In order to facilitate an understanding of the invention, the inlet areas and discharge areas for the track elements 26 and 28, embraced by the solid arrows of FIG. 1, are designated A,. A and A,-', A The spaces between the neighboring inlet areas and discharge areas constitute circular transfer arcs. and are indicated by dashed double-ended arrows 54. 56. S8 and 60. These transfer arcs are the areas between the inlet and discharge passages wherein the fluid between any two vanes must be sealed to prevent communication between the inlet passages and discharge passages in the track elements. Accordingly, the contour of the inner periphery of the track elements in the areas coextensive with the designated transfer arcs are circular arcs so that there is no vane displacement while the vanes are traversing these transfer arcs when the track elements occupy their maximum displacement condition. Stated another way, the track elements are contoured such that when the track elements occupy their respective maximum displacement positions, the transfer arcs are all concentric with the rotor.

If it is envisioned that the pump will be primarily utilized under conditions which permit the track elements to occupy predetermined positions intermediate their maximum displacement and minimum displacement positions, then these transfer arcs should be concentric with the rotor at these predetermined positions for best pump performance. For the purposes of describing the instant invention, we are assuming that the prevalent operating condition will be that of maximum displacement, and thus it is important, in this maximum pressure load condition, to have the transfer arcs concentric with the rotor. Obviously, if these transferarcs are concentric with the rotor in the maximum displacement position of the track elements 26 and 28, then these arcs will not be exactly concentric when the track elements are displaced from their maximum displacement positions. In addition, the length of each of the transfer arcs is at least equal to or greater than one vane spacing; that is,'equal to or greater than the arc distance from a point at the tip of one vane to a corresponding point at the tip of an adjacent vane. The circular contour of the ceiling block in the area of each transfer are and the stated minimum arc length of each transfer are combine to assure that the inlet and discharge passages will be isolated from each other so that leakage therebetween is prevented.

The contours of the inner peripheries 26a and 28a in the areas of the inlet and discharge passages (A,, A, and A,,, A, respectively) are all cam surfaces, and the distance between these surfaces and the outer periphery of the rotor progressively changes along the arcs of these areas. Therefore, there is a net vane displacement as these inlet and discharge areas are traversed by the vanes, and this displacement results in a fluid discharge as each of the discharge areas is traversed and a fluid intake as each of the inlet areas is traversed.

At this point, it would be profitable to describe the operation of the pump as the vanes traverse the vane track or guide defined by the inner peripheries or surfaces 26a and 28a of the track elements. Assuming that the track elements occupy their maximum displacement positions, and that the shaft 20v and the rotor 18 are rotating counterclockwise, the analysis begins with the upper edge of the inlet area A, of track element 26 at its juncture with transfer are 54. Bearing in mind that the contour of track element 26 in the area of transfer are 54 is a circular arc concentric with the rotor, it can be seen that the contour of the inner surface 260 of track element 26 changes from a circular arc to a cam surface at the point of juncture of arrow 54 and the inlet area A,. The contour of the inner periphery of track element 26 in the area A, recedes from the rotor 18 as the inlet area A, is traversed in a counterclockwise direction so that the separation between the rotor 18 the inner periphery 26a of the track element 26 in the inlet area A, increases at successive counterclockwise stations along the inlet area A,. Assuming that the outer ends of the vanes 22 are caused to remain in contact with the inner peripheries of the respective ceiling blocks, either by centrifugal force or fluid pressure under the vanes, each vane is thereby caused to move within its slot in a radially outward fashion from the surface of the rotor 18 as the vane traverses the arc defined by the inlet area A,, and each successive vane in turn in a counterclockwise direction will be in a more extended position than the vane immediately trailing it in the direction of rotation. There is thus a net increase in the volume defined between the side plates 46 and 48 and any two vanes as the vanes move in a counterclockwise direction along the arc of the inlet area A,. Thus, a fluid, such as fuel, made available to the inlet passages 26!; and 26c via inlet conduit 16 and the openings in the frame 30, enters into the intervane volume as the vanes traverse the arc of the inlet area A,. As each vane reaches the end of the arc of inlet area A,, it enters into the area defined as transfer are 60. Bearing in mind that the inner periphery of the track element encompassed by transfer are 60 is a circular are concentric with the rotor surface in the maximum displacement positions of the track elements 26 and 28 (FIG. 1), and that the arc length of transfer are 60 is at least equal to or greater than one vane spacing, the volume between any two vanes (sometimes referred to as the intervane volume) remains constant in traversing arc 60, and the volume is at least momentarily sealed from the inlet area A, and the discharge area A,,'. Because of the fact that the contour of the inner periphery of the track element is a circular are along transfer are 60, there is no attempt to compress the fluid contained in the volume between two successive vanes when traversing the are 60. Thus, a serious overloading of the pump is avoided by this design. It should also be noted that there is no inward or outward movement of the vanes as they traverse are 60 and, therefore, sliding friction loads between the vanes and their respective slots are avoided as the vanes traverse are 60.

The vanes now enter into the arc defined by outlet area A The inner periphery of the track element 28 in the discharge area A, is a cam contour which progressively decreases the distance between the inner periphery 28a of the track element 28 and the surface of the rotor 18 with reference to a counterclockwise direction. Since the separation between the surface 28a and the rotor 18 progressively decreases as the discharge area is traversed in a counterclockwise direction, each vane is cammed inwardly in its slot during traversal of outlet area A,,. Assuming for example that the discharge outlets 28g and 28h of the axial discharge passage 28f are in fluid communication with a load (such as a fuel nozzle or a pressurizing valve), the fluid in an intervane volume will become pressurized as the fluid in the intervane volume traverses transfer are 60 and becomes exposed to the discharge area A,,'; that is, fluidly communicates with the radial discharge passages 28d and 286.

The pressurized fluid then coming within the arc of the discharge area A, will then be forced out through the discharge outlets 28g and 28h via radial discharge passages 28d and 282, and axial discharge passage 28f, as a result of the vanes being displaced inwardly with respect to their slots by the camming action of the cam contour of surface 28a along the arc of discharge area A,,. This inward displacement of the vanes results, of course, in a reduced volume between any two vanes as the vanes move counterclockwise along the arc of discharge area A and the fluid is thereby forced to move from this reduced volume out of radial discharge passages 28d and 28e.

It will be appreciated that the pumping capacity of the pump of FIG. 1 is a direct function of the displacement of the vanes as the vanes traverse discharge area A, and are cammed inwardly therewithin. After traversing the arc of discharge area A each vane then enters into transfer are 58, the inner surface of the track element 28 within transfer are 58 is similar to transfer arc 60 in that it is a circular arc, whereby there is no inward or outward displacement of the vanes as they traverse are 58. The are width of are 58 is also at least equal to or greater than one vane spacing, so that the intervane space between any two successive vanes is at least momentarily sealed as the vanes advance from the end of discharge A, toward the beginning of inlet area A,. Thus, leakage around the rotor between discharge area A, and inlet area A, is thereby avoided.

The contour of the inner periphery 28a of track element 28 in the vicinity ofinlet area A, is, of course, the same as that in the vicinity of inlet area A,; that is, the contour of the inner periphery 28a of track element 28 within the arc of inlet area A, recedes from rotor 18 as the inlet area A, is traversed in a counterclockwise direction. Thus, the inner periphery of track element 28 within the arc of inlet area A, is a cam surface which results in an increasing intervane volume and a consequential drawing of fluid into the increasing intervane volume as the vanes traverse this inlet area in a counterclockwise direction.

Immediately after leaving inlet area A,', each vane passes through another transfer are 56 which, like transfer arcs 60 and 58, is of a circular contour and is at least equal to or greater than one vane spacing so that there is no vane displacement while traversing the transfer arc, and so that the intervane spacing between any two vanes is at least momentarily sealed from both inlet area A, and outlet area A, to prevent leakage therebetween. After traversing transfer are 56, each vane then enters into the arc defined by discharge area A,,. The contour of the inner surface 26a of track element 26 within the arc of discharge area A,,, as is the case with discharge area A,,', is a cam surface which advances towards rotor 18 as the arc is traversed in a counterclockwise direction. Thus, separation between the inner surface 26a of the track element 26 and rotor 18 diminishes as discharge area A, is traversed in a counterclockwise direction, thereby resulting in an inward displacement of each vane in its slot as the vane traverses discharge area A In a manner similar to that previously described with reference to discharge area A,,', the fluid in an intervane volume traversing transfer arc 56 becomes pressurized as the intervane volume comes under the influence of discharge area A The pressurized fluid in the intervane volume is then forced out of the space between the rotor and the inner periphery of the track element in the discharge area as the vanes are inwardly displaced in their slots, and the intervane volume decreases during the traversal of this area. After passing through the arc of discharge area A,,, each vane enters into yet another transfer are 54.

The contour of the inner periphery of the track element 26 encompassed by transfer arc 54 is a circular arc having a width at least equal to or greater than one vane spacing. Thus, as previously described with respect to transfer arcs '60, 58 and 56, transfer are 54 is an area through which the vanes undergo zero radial displacement during movement therein, when the track elements occupy their respective maximum displacement positions as shown in FIG. 1. This arc 54 comprises at least a momentary seal for each intervane volume between the discharge area A,, and the inlet area A,.

It will be appreciated from the foregoing that the described mode of operation relates to a double-acting pump; that is, a pump with two inlet areas and two outlet areas. It will also be apprehended that the two inlet areas'are diametrically opposed, and that the two outlet areas are similarly diametrically opposed, thereby pressure balancing the rotor. It will also be appreciated that for the illustrated pump design, the durability of the pump is enhanced at maximum pressure loads because the transfer arcs 54, 56, 58 and 60 are concentric with the rotor. Further, the foregoing illustrative description of the operation of the pump, as rotor 18 moves in a counterclockwise direction, has been directed to an analysis as a vane or a pair of vanes traverses the vane track defined by the inner peripheries 26a and 28a of the track elements 26 and 28, respectively. It will, of course, be understood that the actions previously described in connection with the inlet and outlet areas, and the transfer arcs occur simultaneously with respect to vanes or sets of vanes around the circumference of the rotor so that the several described inlet discharge and seal transfer actions are all occurring simultaneously. It will also be understood that each inlet area in reality encompasses two passages, as depicted in FIGS. 3 and 4. Thus, the inlet area A, embodies radial inlet passages 26b and 260, and the outlet area A embodies radial outlet passages 26d, 26e.

Turning again briefly to FIG. 2, it can be seen that the outlets 28g and 28h of the axial discharge passage 28f respectively discharge fluid into discharge conduits 62 and 64 via appropriate discharge apertures in side plates 48 and 46. The interrelationship between the side plates 46 and 48 and the track elements is more fully discussed hereinafter.

The smooth contour transition along the inner peripheries of the track elements 26 and 28 result in minimum vane dynamics problems for all displacement conditions and notably that of maximum displacement. As will also be discussed hereinafter, in connection with the bridge structure or area of interdigitation between the track elements 26 and 28, the vane track contour defined by the inner peripheries 26a and 28a is formed to provide smooth transition and preserve minimal vane dynamics, irrespective of the relative position of the track elements between their maximum displacement and minimum displacement positions.

Turning now to FIG. 1A, the pump is now shown with the track elements moved apart to a position wherein the pistons are at their outer limits of travel, and the pump is at a minimum displacement configuration. If desired, movement of just one of the track elements could be used to unload the pump, and this would permit the elimination of one of the cam surfaces 38 and 40 on the actuation ring 32 and one of the pistons 34 and 36. It should be understood that with the arrangement illustrated in FIGS. 1, 1A and 2, the track elements could be caused to assume any position between the loaded position of FIG. 1 and the unloaded position of FIG. 1A for artial loading. While the means shown which moves the track elements is a cam ring incorporating two cam follower members thereupon, it will be appreciated that any actuation structure having a cam surface thereon could be employed to displace the track elements, but that the utilization of two diametrically opposed cam follower members prevents the actuation ring 32 from bearing against the frame and engendering friction which would be detrimental to the control of the pump.

As can be clearly seen in FIGS. 3-5, the track element 26 includes a lip having two grooves intermediate the axial ends thereof, these grooves being designated 26! and 26j. Also included in the track element 26, across from the grooves 261' and 26j on the other lip, are two tongues 26k and 26L. The grooves and the tongue structures in track element 28 are denoted 28i, 28j, 28k and 28L. At this point, it should be noted that the tongues 28k and 28L are adapted to slidingly fit in the grooves 261' and 26j, and that the tongues 26k and 26L are adapted to slidingly fit in the grooves 28i and 28j. It is also important to note thatthe inner periphery of the track elements in the area of the grooves is arcuate and constitutes part of the inlet cam surface. The tongues, however, are flat on their inner peripheries and thus the inner peripheries or surfaces of each tongue define a flat plane or surface. The flat plane of the inner surface of each tongue is arranged to be tangent to the inner periphery of the track element with which it is associated. Stated another way, the inner surface of the tongues is tangent to the inner periphery of their respective associated track elements at the lines of juncture between the tongues and the track elements. Referring to FIG. 5, wherein the track elements 26 and 28 are shown spaced apart from one another in an exploded view, which, of course, is not the case in the actual pump, it can be observed that the inner surface 66 of tongue 28L is tangent to the contour of the inner periphery 2a of the track element 28 at its line ofjuncture 68. Similarly, the inner surface 70 of tongue 26L is tangent to the inner periphery 26a of track element 26 at its line ofjuncture The grooves 26j and 28j shown by the dashed lines in FIG. 5 are adapted to receive the tongues 28L and 26L. With reference to FIG. 5 and FIG. 3, it will be noted that the grooves 26j and mating tongues 28j form part of inlet areas A, and A, by virtue of the recesses at the extremity of the inlet passages adjacent the grooves and the recesses at the tips of the tongues and that during clockwise rotation of the rotor 18, the tip of a vane traveling on the inner periphery 26a of track element 26 will pass over the groove and then contact the inner surface 66 of tongue 28L when the pump is in a minimum displacement condition in which the track elements are spread apart, as shown in FIG. Ia. Similarly, a vane passing over the groove 28] will contact the surface 70 in the FIG. 1A

configuration. The planar inner surfaces 66 and 70 of the tongues 26k and 26L are machined so that the edge of each tongue will not protrude from the periphery 26a in the maximum displacement position to preclude a vane tip from engaging the tip ofa tongue and rendering the pump inoperative. Alter natively, the outer surfaces of the track elements may be machined to insure, this arrangement. It is important to note that the vane always proceeds from a groove to a tongue, as can be seen from FIGS. 1, 1A, and 3-5, when the track elements are in their maximum displacement position, the tips of the tongues of one track element abut the bottoms of the grooves of the other track element and the vanes pass essentially directly from one inner periphery to another inner periphery; that is, from inner periphery 26a directly to inner periphery 28a, and subsequently from inner periphery 28a to inner periphery 26a. However, except in that one condition of maximum displacement, wherein the tongues of one track ele ment are firmly received in the grooves of another track element, the transition of the vvanes from the inner surface of one track element to the inner surface of another track element is guided by the inner flat surface on the tongue of the other track element.

The design of this pump, with its two identical vane track elements, lends itself to fabrication. To insure the proper relationship between the internal contours of the two-vane track elements required for a pump, the final sizing and finishing operations are performed on the pair of vane track elements when they are fixed in the zero displacement position. In this position, the complete contour is exposed. The two-vane track elements are then considered matched pairs.

Referring now to FIG. 6, there is shown a perspective view of the frame 30. The frame 30 comprises a pair of thick walls and 82 which have planar inner surfaces 84 and 86 which are parallel to one another. The inner surfaces 84 and 86 of the frame 30 are adapted to abut the parallel sides (the vertical outer sides of FIG. 5) of the track elements to guide the track elements in their movement between minimum and maximum displacement positions. With reference to FIGS. 4 and 5, it can be seen that the track element 26 comprises a generally flat outer surface 26s which is contacted by the balance piston assembly 242. The balance piston assembly 244 is, of course, adapted to bear against the corresponding surface on track element 28.

As best shown in FIG. 10, the balance piston assembly 242 comprises a piston 90 and pair of spaced legs 92 and 94. The slots 96, 98 in the frame are adapted to slidingly receive the respective legs 92 and 94. The balance piston assembly 244 is identical to balance piston assembly 242, and the depending legs thereof project through slots 100 and 102 of the frame 30 to engage surface 28s ofthe track element 28. The depending legs of the balance piston assemblies straddle the rotatable actuation ring 32 which is disposed intermediate the slots 96 and 98. Between the slots 96 and 98 is another slot 104 which develops into a larger opening I06. Similarly, on the diametrically opposed side of the frame 30, slot 108 is similarly disposed between slots 100 and 102, and similarly develops into a larger opening 110. All of the slots and openings allow fluid to pass radially through the frame to the inlet passages in the track elements.

Although in the schematic view of FIG. 1 the cam member 38 is shown to the left of depending leg 94, for the sake of clarity it will be understood that cam member 38 protrudes through slot 104 and is guided by the sides thereof during rotation of the actuation ring 32. Similarly, cam member 40 on actuation ring 32 protrudes through slot 108 and is guided by the sides thereof during rotation of the actuation ring. It will further be understood from FIGS. 3 through 6 and 10 that the depending legs on the balance pistons not only straddle the actuation ring, but also straddle the cam surfaces on the track elements. The frame 30 also includes two holes 112 and 114, and a similar pair of axially aligned holes on the end of the frame which is not shown. The purpose of these holes is to mount the sideplates 48 and 46.

Turning now to FIGS. 7 through 9, wherein the construction of the two identical sideplates is shown, each sideplate includes a centrally disposed opening I20 through which the splined shaft 20 of FIG. 2 is received. Spaced from the opening are two elongated discharge apertures 122 and 124 which are shaped as the discharge outlets (26g, 26h, 28g, 28h) of the track elements 26 and 28 and are disposed against these discharge outlets in a mating relationship. As shown in FIG. 2, the discharge aperture 124 receives flow from the axial discharge passage 28f of the track element 28 via the discharge outlet 28h. Still referring to FIG. 2, flow from the discharge aperture 124 of sideplate 46 proceeds through discharge conduit 64. Discharge conduits 62 and 64 merge to form a single discharge conduit 64. Discharge conduits 62 and 64 merge to form a single discharge conduit 65. Similarly, flow from discharge outlet 28g proceeds to discharge conduit 62 via discharge aperture 124 of sideplate 48. The respective discharge apertures 122 of the sideplates 48 and 46 similarly receive output flow from axial discharge passage 26f and deliver the output flow to another pair of discharge conduits (not shown) which merge as discharge conduits 62 and 64 into a single conduit which joins conduit 65 in the housing 12.

Spaced from the boundaries of the opening 120 is a circular recess 126 which communicates with discharge pressure via recesses 128 and 130. The recesses 128 and 130 serve to fluidly interconnect the recess 126 with the discharge apertures 122 and 124 respectively, thereby maintaining high pressure in recess 126. As can be seen in FIG. 2, the respective recesses 126 of the sideplates 46 and 48 port discharge pressure to the underside of the vanes via the respective vane slots to keep the vanes in firm contact with the track surface defined by the track elements. In order to prevent this discharge pressure in recess 126 from separating the sideplates from the axial end to the pump, two auxiliary recesses 132 and 134 extend across the sideplate. Thus, if a large pressure develops in recess 126, pressure will not be produced near the edge of the plate (which could possibly lift the plate off the pump), but instead flow will proceed from recess 126 to the recesses 132 and 134 which are referenced to the inlet pressure of cavity 14. Thus, only the area of the sideplate encompassed by the recesses 132 and 134 will be exposed to high pressure. should the discharge pressure in recess 126 rise to a prohibitive value.

Lugs 136 and 138 are secured to the side plate and project axially therefrom and are adapted to be received in the holes 112 and 114 respectively of the frame 30 and the corresponding set of holes on the side of the frame not shown. As previously mentioned, the sideplates are urged into firm engagement with the axial ends of the pump by means of piston 52, and thus the auxiliary recesses 132 and 134 merely provide an extra margin ofsafety.

The control system for the pump 10 is shown schematically in FlG. 1. it should be noted at the outset that although the elements which form the control system are shown located in the housing, they could, if desired, be located in separate housings and interconnected by suitable conduits. The basic elements of the control system for the illustrated pump are a servo valve, generally designated at 140, which forms the heart of the control system, a wash flow filter 142, which filters the output flow for certain control functions, and a needle type pressure relief pilot valve 144, which prevents the output pressure from reaching a predetermined value by controlling leakage across the sideplate 48.

Referring again briefly to FIG. 2, it can be seen that discharge conduits 62 and 64 join to form a single conduit 65 which directs output flow to the wash flow filter 142. It will be remembered that the pump also includes two other discharge conduits (not shown) which merge into a single discharge conduit. these conduits communicating with the axial discharge passage 26f of the track element 28 via the respective discharge apertures 122 of the side plates 46 and 48. This single discharge conduit joins with the discharge conduit 65 upstream of the wash flow filter 142. Thus, the wash flow filter 142 receives the output flow from four discharge conduits in the pump housing, two of which are 62 and 64.

Flow passes axially through the wash flow filter 142, which is a generally cylindrical structure, to a main discharge conduit 146. Main discharge conduit 146 could be connected to the inlet ofa fuel control or another type of control depending on the application for which the pump is selected. Fluid, which enters the filter and does not pass therefrom to main discharge conduit 146, passes radially through the filter element 148 into an annular chamber 150. Two conduits 152 and 154 communicate with this annular chamber for carrying filtered output flow to various elements in the control system. Conduit 152 carries filtered output flow to the outer face of balance piston 90, and conduit 154 carries output flow to the outer face of the balance piston assembly 224 via a secondary conduit 156. Thus, pump discharge pressure urges the legs of the balance pistons against the tract elements to urge the track elements in the direction of the rotor. Of course, this pressure will not physically move the track elements, but will merely render it easier for the actuation ring to control the displacement of the pump as previously described.

A branch conduit 158 communicates with conduit 152 to carry filtered discharge flow to pressure relief valve 144 and the outer face of piston 52, the discharge flow being communicated to the outer face of the piston 52 via conduit 160, which is also shown in FIG. 2. Conduit 158 embodies an orifice 162 which permits the pressure, communicated to the outer face of piston 52, to be slightly below that of the discharge. The pilot-operated relief valve 12 is a spring-biased needle valve which includes a piston 162 which is urged downwardly within its cylinder by a compression spring 164. On the lower face of piston 162 is secured a needlelike shaft 166 which controls the flow from conduit 158 to a return conduit 168 which communicates with the inlet conduit 16. Conduits 170 and 172 respectively interconnect conduits 158 and 168 with the cylinder of relief valve 12 at respective locations below the lower face of piston 162 and above the upper face of piston 162. Thus, if a discharge pressure should exceed a predetermined value, the force exerted upon the piston by the pressure communicated via conduit 158 and conduit 170 will overcome the bias provided by the spring 164and the inlet pressure acting on the upper face of the piston 162. thereby causing the piston 162 to rise vertically in its housing and permitting fluid communication between conduits 158 and 168. The orifice developed between the needle valve and its seat operates in conjunction with orifice 162 to schedule the pressure to the piston 52 (via conduit 160) and thereby achieve a force balance across the sideplate 48 to permit it to float, this floating maintaining the maximum pressure differential by a controlled internal leakage across the sideplate 48.

The servo valve 140 is the heart of the control system in that it is the mechanism by which the actuation ring is controlled, and hence controls the displacement of the pump. Each of the actuator piston assemblies 34 and 36 includes a piston 174 which is slideably mounted within a suitable cylindrical cavity and is attached to a shaft 176. The shafts 176 are pivotally connected to the links 178 which in turn are pivotally connected to the actuation ring 32 at diametrically opposed locations. The diametrically opposed locations on the actuation ring, to which the shafts 176 are respectively connected, insure that the actuation ring 32 will not bear against the frame 30 when rotated, but will only be guided thereby. The arrangement contributes to maintaining friction between the actuation ring 32 and the frame 30 at a minimum value. The inner and outer faces 180 and 182 respectively of the piston 174 are exposed to pressures which create an axial force imbalance on the piston 174 to displace the piston or hold it in a fixed position. The inner faces of the pistons are in communication with an interconnecting conduit 184 which is connected to the servo valve 140. The outer faces of the pistons of the actuator piston assemblies are interconnected in a like manner by interconnecting conduit 186. The interconnecting conduits 184 and 186 are fluidly connected to the servo valve, as is described hereinafter.

The servo valve per se comprises a spool having four lands 188, 190, 192 and 194, the spool being slideably disposed within a bore 196. The bore 196 comprises two main ports 198 and 200 which respectively communicate with the interconnecting conduits 184 and 186. Bore 196 also includes secondary ports 202, 204, 206 and 208. The ports 202 and 206 communicate with this annular inlet area via conduit 210 and branch conduits 212 and 214. Port 204 communicates with discharge pressure via conduit 154. Normally, the spool will be disposed within the bore 196 such that land covers port 198 and land 200 covers port 208. in this condition, the other ports 202, 204 and 206 will communicate with the annular spaces defined between the lands of the spool. Connected to the left end of the spool is a bellows 216 which is housed within a cavity 218 which comprises an annular abutment 220 to which the bellows 216 is secured by a weld 211. A bore, which communicates with the left end of the cavity 218, threadingly receives a setscrew 222. A compression spring 224 is interposed between the left end of the bellows and the setscrew to bias the bellows in the direction of the spool. That portion of the cavity 218 to the left of the annular abutment 220 is in communication with a signal conduit 226 which is adapted to receive a signal pressure, and the other portion of the chamber 218 to the right of the annular abutment 220 is in communication with another signal conduit 228. Signal conduit 228 also communicates with port 208 to transmit the pressure therein to the outboard face of land 194.

The pressure in signal conduit 228 is maintained at a predetermined value above that in conduit 226 to maintain the spool in the position in which the actuator pistons are maintained in an equilibrium position, this being the illustrated position. If desired, this differential pressure between the signal conduits 226 and 228 which maintains the spool in a neutral position may be varied by means of setscrew 220. Assuming that it is desired to displace the track elements 26 and 28 to their minimum displacement positions, as shown in FIG. 10, it is necessary to increase the differential pressure between the signal conduits 226 and 228. Increasing the pressure in signal conduit 228 creates a force imbalance on the spool and the bellows which shifts the spool to the left, thereby directing high pressure into interconnecting conduit 184 via conduit 154, port 204 and port 198. Simultaneously, the pressure in conduit 184 is decreased as port 200, which is in communication therewith, now communicates with port 206 via the annular space between lands 192 and 194. Thus, the pressure in conduit 184 increases and the pressure in conduit 186 decreases, thereby producing a forced imbalance across the actuator pistons 174 of the actuator piston assemblies 34 and 36. This forced imbalance causes the pistons 174 of the respective actuator assemblies to move outwardly, and thereby rotate the actuation ring 32 in a clockwise direction. This rotation will continue until the spool returns to its original position, or the pistons 174 reach their limits of travel within their respective cylinders.

Since the pressure between the surface of the rotor and the inner peripheries of the track elements is constantly urging the track elements apart, the respective cam surfaces on the track elements remain in contact with the cam members on the ac tuation ring during rotation of the actuation ring. The track elements thus move outwardly from the rotor to their minimum displacement positions. If it is desired that the track elements be stopped in their outward movement in an intermediate position, the signal pressure in signal conduit 228 must be restored to its original value before the track elements have passed this position. It will be appreciated that the servo valve illustrated provides only open loop control, but that if desired a closed-loop system can be readily incorporated, as will be apprehended by those skilled in the art.

In order to displace the track elements from their minimum displacement positions of FIG. 1a to their maximum displacement positions of FIG. 1, it is necessary to decrease the pressure in signal conduit 228 to cause the spool to shift to the right. Once the spool is shifted to the right, port 198 communicates with inlet pressure via branch conduit 212 and conduit 210, and hence interconnecting conduit 184 communicates with this inlet pressure. Simultaneously, conduit 186 communicates with discharge pressure via port 200, the annular space between lands 190 and 192, port 204 and conduit 154. Thus, a force imbalance will be produced across piston 174 which will produce downward movement of the piston, thereby rotating the actuation ring 32 in a counterclockwise manner. This counterclockwise rotation, of course, displaces the cam blocks inwardly towards the rotor and increases the overall pump displacement.

If desired, filtered discharge flow may be employed to lubricate the bearings of the shaft 20. If this is the case, a suitable conduit, such as conduit 230, may be employed to port lubricating flow to the bearings.

By way of general comment, the pump shown and described has minimal rotor bearing loads and controlled radial vane movement to minimize the instability in dynamic loading of the vanes. Since the vane dynamics in the illustrated pump are not severe, the ump is ada ted to be driven at a high r.p.m.

It will be un erstood, 0 course, that while the orm of the invention shown and described herein constitutes the preferred embodiment of the invention, it is not intended herein to illustrate all of the possible and equivalent forms or ramifications of the invention which fall within the scope of the subjoined claims. It will also be understood that the words used are words of description rather than of limitation, in that various changes, such as changes in shape, relative size and arrangement of the parts, may be substituted without departing from the spirit and scope of the invention herein disclosed. For example, the vanes shown may be replaced by step vanes, and the sideplates thereof may be accordingly modified such that inlet pressure discharge pressure, a combination of both, may be introduced into the vane step areas to control the pressure loading between the vanes and the track elements to assure mechanical efficiency and reduced wear. Further, the illustrated servo valve could readily be replaced by other types of servo valves wellknown to those skilled in the art.

What is claimed is:

1. in a variable displacement vane pump, the combination comprising:

a housing;

a rotor mounted for rotation in the housing;

a plurality of spaced, radially movable vanes mounted on the periphery of the rotor;

a first track element movably mounted in the housing around the periphery of the rotor, the inner surface of the first track element providing a contoured track surface for contacting the tips of the vanes during rotation of the rotor;

a first cam surface on the outer periphery of the first track element;

a second track element movably mounted in the housing around the periphery of the rotor diametrically opposite the first track element, the inner surface of the second track element providing a contoured track surface for contacting the tips of the vanes during rotation of the rotor;

a second cam surface on the outer periphery of the second track element in diametrically opposed relationship to the first cam surface;

an actuation ring mounted for rotation in the housing in surrounding relationship to the track elements;

means to guide the rotation of the actuation ring about an axis coaxial with the rotor;

first and second cam follower members mounted on the actuation ring in diametrically opposed relationship such that the first and second cam follower members respectively contact the first and second cam surfaces for urging the track elements toward the rotor;

balance assembly means to bear against the track elements for urging the track elements toward the rotor to facilitate rotation of the actuation ring and thereby displacement of the track elements by the cam follower members; and

first and second actuator assemblies mounted in the housing and respectively connected to the actuation ring at diametrically opposed locations thereon for rotating the actuation ring such that the ring does not bear against the guide means when rotated by the actuator assemblies.

2. The combination as defined in claim 1 wherein the guide means comprises:

a cylindrical frame mounted within the housing, the ring being mounted around the frame such that it is guided thereby; and wherein:

the track elements are slideably mounted within the frame.

3. The combination as defined in claim 1 wherein each actuator assembly includes:

a piston slideably mounted in the housing; and

a shaft on the piston pivotally connected to the actuation ring.

nuna. 

1. In a variable displacement vane pump, the combination comprising: a housing; a rotor mounted for rotation in the housing; a plurality of spaced, radially movable vanes mounted on the periphery of the rotor; a first track element movably mounted in the housing around the periphery of the rotor, the inner surface of the first track element providing a contoured track surface for contacting the tips of the vanes during rotation of the rotor; a first cam surface on the outer periphery of the first track element; a second track element movably mounted in the housing around the periphery of the rotor diametrically opposite the first track element, the inner surface of the second track element providing a contoured track surface for contacting the tips of the vanes during rotation of the rotor; a second cam surface on the outer periphery of the second track element in diametrically opposed relationship to the first cam surface; an actuation ring mounted for rotation in the housing in surrounding relationship to the track elements; means to guide the rotation of the actuation ring about an axis coaxial with the rotor; first and second cam follower members mounted on the actuation ring in diametrically opposed relationship such that the first and second cam follower members respectively contact the first and secOnd cam surfaces for urging the track elements toward the rotor; balance assembly means to bear against the track elements for urging the track elements toward the rotor to facilitate rotation of the actuation ring and thereby displacement of the track elements by the cam follower members; and first and second actuator assemblies mounted in the housing and respectively connected to the actuation ring at diametrically opposed locations thereon for rotating the actuation ring such that the ring does not bear against the guide means when rotated by the actuator assemblies.
 2. The combination as defined in claim 1 wherein the guide means comprises: a cylindrical frame mounted within the housing, the ring being mounted around the frame such that it is guided thereby; and wherein: the track elements are slideably mounted within the frame.
 3. The combination as defined in claim 1 wherein each actuator assembly includes: a piston slideably mounted in the housing; and a shaft on the piston pivotally connected to the actuation ring. 